[9] When copper is dissolved in dilute nitrous acid, certain quantities of nitrogene are generally produced, likewise the nitrous gas carries off in solution some nitrous acid. [10] This airholder, considered as a pneumatic instrument, is of greater importance, and capable of a more extensive application than any other. It was invented by Mr. W. CLAYFIELD, and in its form is analogous to Mr. WATT’S hydraulic bellows, consisting of a glass bell playing under the pressure of the atmosphere, in a space between two cylinders filled with mercury. A particular account of it will be given in the appendix. They were weighed in a glass globe, of the capacity of 108 cubic inches, which with the small glass stop-cock affixed to it, was equal, when filled with atmospheric air, to 1755 grains. The balance that I employed, when loaded with a pound, turned with less than one eighth of a grain. Into a mercurial airholder, of the capacity of 200 cubic inches, 160 cubic inches of nitrous gas were thrown from a solution of mercury in nitrous acid. 70 measures of this were agitated for some minutes in a solution of sulphate of iron,[11] till the diminution was complete. The nitrogene remaining hardly filled a measure; and if we suppose with Humbolt[12] that a very small portion of it was absorbed with the nitrous gas, the whole quantity it contained may be estimated at 0,0142, or ¹/₇₀. [11] This absorption will be hereafter particularly treated of. [12] Annales de Chimie. Tome xviii. page 139. 75 cubic inches received from the airholder into an exhausted balloon, increased it in weight 25,5 grains; thermometer being 56°, and barometer 30,9. And allowing for the small quantity of nitrogene in the gas, 100 cubic inches of it will weigh 34.3 grains. One hundred and thirty cubic inches of oxygene were procured from oxide of manganese and sulphuric acid, by heat, and received in another mercurial airholder. 10 measures of it, mingled with 26 of the nitrous gas, gave, after the residuum was exposed to solution of sulphate of iron, rather more than one measure. Hence we may conclude that it contained about 0,1 nitrogene. 60 cubic inches of it weighed 20,75 grains; and accounting for the nitrogene contained in these, 100 grains of pure oxygene will weigh 35,09 grains. Atmospherical air was decomposed by nitrous gas in excess; and the residuum washed with solution of sulphate of iron till the Nitrogene remained pure; 87 cubic inches of it weighed 26,5 grains, thermometer being 48°, barometer 30,1; 100 will consequently weigh 30,45. 90 cubic inches of the air of the laboratory not deprived of its carbonic acid, weighed 28,75 grains; thermometer 53, barometer 30: 100 cubic inches will consequently weigh 31,9.[13] 16 measures of this air, with 16 nitrous gas, of known composition, diminished to 19. Hence it contained about,26 oxygene.[14]